Laminated glass windscreen intended to be used at the same time as a HUD system reflector

ABSTRACT

A laminated safety glass windscreen, which can also be used as a reflector in a HUD system, comprises at least first and second panes and a thermoplastic intermediate layer which joins these panes together. The cross-section of the intermediate layer is in the shape of a wedge, decreasing in thickness from top to bottom. The thermoplastic intermediate layer may be composed of two sheets, one of which is provided with a colored filtering strip and has a wedged cross-section conditioned by the appearance of this filtering strip. The other sheet has a wedged cross-section such that the two sheets together have the prescribed convergence angle for using the windscreen as a reflector.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a laminated glass windscreen having apredetermined taper angle and intended to be used at the same time as areflector in a HUD system.

2. Discussion of the Background

It is known that the reflection of light rays from the surfaces of glassincreases with the angle of incidence. In the case of windscreens whichare fitted with a large angle of inclination, objects situated insidethe vehicle and below the windscreen are visible to the driver in thewindscreen, which acts as a mirror. This effect can be exploited, forexample by projecting optical information onto the windscreen. In thisregard, however, ordinary windscreens with parallel faces present theproblem that the light rays, which are reflected both by the interiorsurface and by the exterior surface of the windscreen, present theobserver with two images which are offset relative to one another.

It is known from EP 0 420 228 B1, hereby incorporated by reference, thatthis problem of double images can be avoided by using an intermediatelayer with a wedge-shaped cross-section which makes the two reflectingsurfaces of the windscreen form an angle such that the two reflectedimages appear superimposed to the driver's eyes. In this way, not onlyis a relatively sharp reflected image obtained, but the clarity of theimage is also enhanced. However, the taper angle required of theintermediate layer for this purpose depends strongly on the angle atwhich the windscreen is fitted and on the position of the imageprojector in the vehicle, and therefore needs to be carefully adapted toeach particular situation.

It is also known to use a thermoplastic intermediate sheet with a tintedfiltering band during the manufacture of curved windscreens made oflaminated glass with a filtering strip along the upper edge. The desiredcurvature of the filtering strip is then obtained by intentionalirregular stretching of the sheet. This stretching, involving plasticdeformation of the sheet, is carried out in order to adapt the profileof the filtering strip to that of the upper part of the laminatedwindscreen. Stretching in the shape of a circular arc leads to a taperon the long side of the curvature, which gives a sheet with awedge-shaped cross-section. The taper angle of a sheet stretched in thisway is determined by the radius required for the filtering strip.Therefore, the thermoplastic sheet with wedge-shaped cross-sectionformed in this way does not normally have the taper angle needed for awindscreen to be used as a reflector in a head-up display (HUD) systemcomprising two reflection surfaces which form a determined angle inorder to superimpose the images.

SUMMARY OF THE INVENTION

An object of the invention is to provide a laminated glass window whichcontains a tinted filtering strip integrated with the thermoplasticintermediate sheet, whose curvature is adapted to that of the upper edgeof the laminated glass pane and whose two panes also form, relative toone another, an angle such that they serve as a reflector in a head-updisplay system, resulting in two reflected images which are superimposedwith a view to enhancing brightness and avoiding a double image.

This object is achieved with an intermediate layer comprising at leasttwo thermoplastic sheets, one of which is provided along its upper edgewith a tinted filtering strip, and the other has a wedge-shapedcross-section such that the two sheets together have the desired taperangle.

BRIEF DESCRIPTION OF THE DRAWINGS

Various other objects, features and attendant advantages of the presentinvention will be more fully appreciated as the same becomes betterunderstood from the following detailed description when considered inconnection with the accompanying drawings in which like referencecharacters designate like or corresponding parts throughout the severalviews and wherein:

FIG. 1 is a front view of a windscreen with a tinted filtering strip,and

FIG. 2 is a view in section on the axis II-II in FIG. 1.

FIG. 3 is a view in section on the axis II-II in FIG. 1, of anembodiment different from that of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

A laminated glass window according to the invention has the advantagethat the two reflecting surfaces can be arranged relative to one anotherwith a predetermined taper angle, with a view to using the windscreen asa reflector in a HUD system, irrespective of the taper angle alreadypresented by the thermoplastic sheet with the incorporated tintedfiltering strip.

It is also possible for the laminated glass windscreen to have astraight edge at the filtering strip. In this case, the sheet comprisingthe filtering strip does not need to be stretched, and consequently nolonger has a wedge-shaped cross-section. The required taper angle isthen produced only by the other sheet.

According to a further advantageous embodiment of the invention, asupport sheet comprising a functional layer is placed between thethermoplastic sheets which together form the defined taper angle. Thissupport sheet may, for example, be made of polyethylene terephthalate(PET) and be provided with a coating which reflects infraredwavelengths, but is transparent to other wavelengths.

The taper angles required of the thermoplastic sheets may be obtained bystretching with plastic deformation, but it is also possible to usesheets originally extruded with a wedge-shaped cross-section. The sheetprovided with the tinted filtering strip may itself also be extrudedwith a wedge-shaped cross-section.

When the sheets are being drawn to give them the necessary radii ofcurvature, which may be as little as 2 m, it is clearly necessary totake care that the two sheets together have a minimum thickness in orderto retain a safety functions and adhesion properties. A person ofordinary skill in the art can easily select a suitable thickness for thesheets.

A variety of commercially available polymer sheets may be used asthermoplastic sheets which together are to form the determined taperangle. In particular, polyvinyl butyral and polyurethane sheets aresuitable.

Having generally described this invention, a further understanding canbe obtained by reference to certain specific examples which are providedherein for purposes of illustration only and are not intended to belimiting unless otherwise specified.

Referring to FIG. 1, the windscreen 1 is provided along its upper edgewith a tinted filtering strip 2. As illustrated in FIG. 2, thiswindscreen may be produced with a taper angle θ in order to ensuresuperimposed reflection of an image by the exterior surfaces 33 and 61of the panes 3 and 6. In this example, the taper angle θ is selected tobe 0.5 mrad.

At its upper edge, the laminated glass windscreen 1 has a radius R₁ of3.30 m, and its height h is 0.80 m. The thermoplastic sheet 4 comprisingthe tinted filtering strip 2 is made of polyvinyl butyral (PVB).Initially, it has an overall thickness and, after drawing on its upperedge, of 0.76 mm (d₁). From the geometrical ratios and prescribed data,it is possible to deduce the taper angle k₁ which is obtained bystretching the PVB sheet 4 with the desired radius of curvature R₁,using the formula: $k_{1} = \frac{d_{1}}{R_{1} + h}$where d₁ is the initial thickness of the sheet, R₁ is the radius ofcurvature at the upper edge, and h is the height of the sheet, whichgives k₁=0.185 mrad.

In order to obtain the required taper angle θ of 0.5 mrad, it isnecessary to add a second thermoplastic sheet 5, also made of PVB,having a taper angle k₂ of 0.315 mrad, such that 0.5 mrad=θ=k₁+k₂. Foran initial thickness d₂=1.52 mm of the second sheet, the relation:$R_{2} = {\frac{d_{2}}{k_{2}} - h}$gives, for this sheet, a required stretching radius of 4.025 m.

The two stretched thermoplastic sheets 4 and 5 are arranged in such away that the taper angles k₁ and k₂ are added to give the stipulatedangle of θ=0.5 mrad. The sheets are then assembled in the conventionalway with the curved panes 3 and 6 to form a laminated glass windscreenwhich exhibits the required taper angle of 0.5 mrad.

The specific values R₁, h, and d₁ are easily selected by those ofordinary skill in the art, and in part depend on dimensions of thespecific vehicle in which the windscreen is intended to be used. As anexample, R₁ may be 2-4 m, h may be 0.40-1.6 m, and d₁ may be 0.10-2.50mm. Similarly d₂ may be 0.10-2.50 mm.

A third sheet may be included, such as a support sheet comprising afunctional layer between the thermoplastic sheets. Such an embodiment isillustrated in FIG. 3, where the support sheet 7, is between thethermoplastic sheets 4 and 5.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

The priority document of the present application, German PatentApplication No. 197 31 873.8, filed on Jul. 24, 1997, is herebyincorporated by reference.

1. A laminated glass windscreen having a taper angle for a reflector ina HUD system, comprising: (i) a first pane, (ii) a second pane, and(iii) a intermediate layer having a wedge-shaped cross-section, betweensaid first and second panes, comprising (a) a first thermoplastic sheetcomprising a tinted filtering strip at an upper edge of said firstthermoplastic sheet, and (b) a second thermoplastic sheet, on said firstthermoplastic sheet, wherein said second thermoplastic sheet has awedge-shaped cross-section; wherein said first thermoplastic sheet has ataper angle k₁, and said second thermoplastic sheet has a taper anglek₂, wherein the taper angle of said combined sheets (k₁+k₂) is 0.5 mrad,and wherein at least one of either the first thermoplastic sheet or thesecond thermoplastic sheet has a wedge-shaped cross-section.
 2. Thelaminated glass windscreen of claim 1, wherein said first thermoplasticsheet has a taper angle of
 0. 3. The laminated glass windscreen of claim1, wherein said first thermoplastic sheet has a wedge-shapedcross-section.
 4. The laminated glass windscreen of claim 1, whereinsaid intermediate layer further comprises a support sheet comprising afunctional layer, between said first thermoplastic sheet and said secondthermoplastic sheet.
 5. The laminated glass windscreen of claim 1,wherein said first thermoplastic sheet comprises a polymer selected fromthe group consisting of polyvinyl butyral and polyurethane.
 6. Thelaminated glass windscreen of claim 1, wherein said second thermoplasticsheet comprises a polymer selected from the group consisting ofpolyvinyl butyral and polyurethane.
 7. The laminated glass windscreen ofclaim 5, wherein said second thermoplastic sheet comprises a polymerselected from the group consisting of polyvinyl butyral andpolyurethane.
 8. The laminated glass windscreen of claim 1, wherein saidfirst thermoplastic sheet comprises polyvinyl butyral, and said secondthermoplastic sheet comprises polyvinyl butyral.
 9. The laminated glasswindscreen of claim 4, wherein said support sheet comprises polyethyleneterephthalate.
 10. A method of making the laminated glass windscreen ofclaim 1, comprising: laminating said first pane, said intermediate layerand said second pane.
 11. The method of claim 10, further comprising,prior to said laminating, stretching to form said first thermoplasticsheet with a wedge-shaped cross-section.
 12. The method of claim 10,further comprising, prior to said laminating, extruding to form saidsecond thermoplastic sheet in a wedge shape.
 13. The method of claim 11,further comprising, prior to said laminating, extruding to form saidsecond thermoplastic sheet in a wedge shape.
 14. The method of claim 10,further comprising, prior to said laminating, stretching to form saidsecond thermoplastic sheet with a wedge-shaped cross-section.
 15. Themethod of claim 11, further comprising, prior to said laminating,stretching to form said second thermoplastic sheet with a wedge-shapedcross-section.
 16. A method of making the laminated glass windscreen ofclaim 4, comprising: laminating said first pane, said intermediate layerand said second pane.
 17. A method of displaying an image, comprising:projecting an image on the laminated glass windscreen of claim
 1. 18. Amethod of displaying an image, comprising: projecting an image on thelaminated glass windscreen of claim
 4. 19. A vehicle, including thelaminated glass windscreen of claim
 1. 20. A method of displaying animage, comprising: projecting an image on a windscreen of a vehicle,wherein said windscreen is the laminated glass windscreen of claim 1,and reflections of said image from said first pane and said second paneappear superimposed to a driver of said vehicle.
 21. The laminated glasswindscreen of claim 1, wherein said second thermoplastic sheet (b) isuntinted.
 22. The laminated glass windscreen of claim 1, wherein k₁ is0.185 mrad and k₂ is 0.315 mrad.